//手写实现myPromise源码
const PENDING = 'pending' // 等待
const FULFILLED = 'fulfilled' // 成功
const REJECTED = 'rejected' // 失败

class MyPromise {
    constructor(executor) {
        try {
            executor(this.resolve, this.reject)
        } catch (e) {
            this.reject(e)
        }
    }

    // Promise状态
    status = PENDING

    // 成功之后的值
    value = undefined

    // 失败之后的原因
    reason = undefined

    // 成功回调
    successCallback = []

    // 失败回调
    failCallback = []

    resolve = value => {
        // 如果状态不是等待，阻止程序向下执行
        if (this.status !== PENDING) return
        // 将状态改为成功
        this.status = FULFILLED
        // 保存成功之后的值
        this.value = value
        // 判断成功回调是否存在，如果存在，则调用成功回调
        // this.successCallback && this.successCallback(value)
        while (this.successCallback.length !== 0) this.successCallback.shift()()
    }

    reject = reason => {
        // 如果状态不是等待，阻止程序向下执行
        if (this.status !== PENDING) return
        // 将状态改为失败
        this.status = REJECTED
        // 保存失败之后的原因
        this.reason = reason
        // 判断失败回调是否存在，如果存在，则调用失败回调
        // this.failCallback && this.failCallback(reason)
        while (this.failCallback.length !== 0) this.failCallback.shift()()
    }

    then(successCallback, failCallback) {
        successCallback = successCallback ? successCallback : value => value
        failCallback = failCallback ? failCallback : reason => reason
        let promise2 = new MyPromise((resolve, reject) => {
            // 判断状态
            if (this.status === FULFILLED) {
                // 此处使用setTimeout是为了变成异步代码，才会有promise2，同步的话promise2还没生成。
                setTimeout(() => {
                    try {
                        let x = successCallback(this.value)
                        // 判断x的值是普通值还是promise对象
                        // 如果是普通值，直接调用resolve
                        // 如果是promise对象，查看promise对象返回的结果
                        // 再根据promise对象返回的结果，决定调用resolve还是调用reject
                        resolvePromise(promise2, x, resolve, reject)
                    } catch (e) {
                        reject(e)
                    }
                }, 0)
            } else if (this.status === REJECTED) {
                setTimeout(() => {
                    try {
                        let x = failCallback(this.reason)
                        // 判断x的值是普通值还是promise对象
                        // 如果是普通值，直接调用resolve
                        // 如果是promise对象，查看promise对象返回的结果
                        // 再根据promise对象返回的结果，决定调用resolve还是调用reject
                        resolvePromise(promise2, x, resolve, reject)
                    } catch (e) {
                        reject(e)
                    }
                }, 0)
            } else {
                this.successCallback.push(() => {
                    setTimeout(() => {
                        try {
                            let x = successCallback(this.value)
                            // 判断x的值是普通值还是promise对象
                            // 如果是普通值，直接调用resolve
                            // 如果是promise对象，查看promise对象返回的结果
                            // 再根据promise对象返回的结果，决定调用resolve还是调用reject
                            resolvePromise(promise2, x, resolve, reject)
                        } catch (e) {
                            reject(e)
                        }
                    }, 0)
                })
                this.failCallback.push(() => {
                    setTimeout(() => {
                        try {
                            let x = failCallback(this.reason)
                            // 判断x的值是普通值还是promise对象
                            // 如果是普通值，直接调用resolve
                            // 如果是promise对象，查看promise对象返回的结果
                            // 再根据promise对象返回的结果，决定调用resolve还是调用reject
                            resolvePromise(promise2, x, resolve, reject)
                        } catch (e) {
                            reject(e)
                        }
                    }, 0)
                })
            }
        })
        return promise2
    }

    catch (failCallback) {
        return this.then(undefined, failCallback)
    } finally(callback) {
        return this.then(value => {
            return MyPromise.resolve(callback()).then(() => value)
        }, reason => {
            return MyPromise.resolve(callback()).then(() => {
                throw reason
            })
        })
    }

    static all(arr) {
        let result = []
        let index = 0
        return new MyPromise((resolve, reject) => {
            function addData(key, value) {
                result[key] = value
                index++
                if (index === arr.length) {
                    resolve(result)
                }
            }
            for (let i = 0; i < arr.length; i++) {
                let current = arr[i]
                if (current instanceof MyPromise) {
                    // promise对象
                    current.then(value => addData(i, value), (reason) => reject(reason))
                } else {
                    // 普通值
                    addData(i, arr[i])
                }
            }
        })
    }

    static resolve(p) {
        if (p instanceof MyPromise) return p
        return new MyPromise(resolve => resolve(p))
    }

}

function resolvePromise(promise2, x, resolve, reject) {
    if (promise2 === x) {
        return reject(new TypeError('Chaining cycle detected for promise #<MyPromise>'))
    }
    if (x instanceof MyPromise) {
        // promise 对象
        x.then(resolve, reject)
    } else {
        // 普通值
        resolve(x)
    }
}

module.exports = MyPromise